A subjective optometer is an apparatus that presents visual targets (eye charts) to an eye and examines visual functions of the eye based on responses regarding visual performance from a subject.
A human eye has a function that tries to obtain a clear vision of a visual target (that is, tries to focus on the visual target) by adjusting thickness of a crystalline lens. The degree of this visual function is accommodation ability. In an accommodation ability test for measuring accommodation ability by using a subjective optometer, an accommodation ability test is carried out by means of spherical lenses. This method presents visual targets to an eye, sequentially varies spherical powers of the spherical lenses arranged on measuring optical axis, and measures accommodation ability of the eye based on the spherical power applied when the eye becomes incapable of focusing on the visual targets (that is, when the subject answers that he cannot see the visual targets clearly).